Damage engine

[Lukasz A.]

Hello Boys
Colleagues, I have a problem. It is possible that he was moved by the topic, but look for it in a foreign language would take me forever. Plain bearing on the crankshaft was damaged. And now the question. The crankshaft is nitrided? Some people on my forum say it is nitrided, others do not. Can it be sanded? I wonder if the nominal crankshaft seek to repair the old one.
I am giving you a link to a forum where there are pictures, because I can not find them at home on the hard disk.
http://www.forum.alfaholicy.org/nasz...lukasz-37.html
Post no.365
Thank you in advance for all the information and I apologize if this topic has already been.
Regards
Lukas

[Steve Webb]

Hi Lukasz,

so your main bearing are knackered (very knackered from the look of the pics on the other forum) and you want to know if you can regrind the crank and fit oversize bearings. And you also want to know if the crank is Nitrided.

Well on Guy Crofts forum he indicates that the crank is indeed nitrided, or has been sujected to nitrocarburising to give it its full name.

See this thread : http://www.guy-croft.com/viewtopic.php?f=13&t=1670

You can read all about nitrocarburising here : http://en.wikipedia.org/wiki/Ferritic_nitrocarburizing

However you can get hold of oversized main bearings, plenty on this page http://www.deltaintegrale.com/catalo...lv=3&C1=2&C2=2

So i would say that regrinding the crank, provided it isn't too damaged is an option rather than having to get hold of a new one.

[Lukasz A.]

Thx Steve.
I'll try to grind the crankshaft,but I'm affraid that damage of rod bearing will come again because I don't know how deep is the oxide layer.If I'll grind too much problem back but for brave people,world belong
I have to grind the cylinder surface too,because piston had big clearance on crank and made some scratches on it.
Main and rod bearings I'll buy in Poland it's no problem with it.
Just need to know.Can I grind the crankshaft or not? Anyone did it?Everything is ok after all? Do I have to nitrited crankshaft after grinding?

[Evodelta]

Check the crank for bow (bend), when a crank destroys bearings to such a degree that is your biggest problem: The crank will probably be bent.
It takes a lot of measuring, knowledge and experience to know when a crank can be reground and reused and to do it, not for the average man on the street, I would recommend a new or good used crank.

[Lukasz A.]

Thx Evodelta

I think it's gonna be too much work with the old one.Cranckshaft grinding,nitriding and alingmnent.Too much time and money to spend for it and not sure that it will work correctly.
I've made decision.I'll look for a good used crankshaft

[hf hpe]

this is from Integrale manuals

[Steve Webb]

Interesting exert from the manual there. The bit that stands out for me is "When the crankpins or main journals have to be ground , after undersizes the shaft should once again undergo nitriding"

The way I read this is that the original nitriding exists down to a surface depth sufficient to let you regrind the crank to use the standard oversized bearings. If you go beyond the standard oversizes (0.6mm over??) then you need to renitride.

What does everyone else think?

[SteveNZ]

No, you'll need to re-nitride the crank even for the first undersize.

[Evodelta]

Interesting exert from the manual there. The bit that stands out for me is "When the crankpins or main journals have to be ground , after undersizes the shaft should once again undergo nitriding"

The way I read this is that the original nitriding exists down to a surface depth sufficient to let you regrind the crank to use the standard oversized bearings. If you go beyond the standard oversizes (0.6mm over??) then you need to renitride.

What does everyone else think?

To a certain extent yes, but to know for certain you need to be able to check it and I doubt you would get to .6, that's too far.

We did regrind a crank and check it for hardness, it got harder as we went deeper in and then suddenly went soft, I would say it went harder probably because of the 'work hardening' effect which occurs on some kinds of metals.

It's also worthy of note that the process does not always penetrate equally so you can be soft on one side and hard on the other.

Re-nitriding is inadvisable as the crank usually bends due to the imbalance of surface treatments/and or bad processing, we proved this. If I had to (and I have no reason to given the amount of new and used cranks still openly available) I would have a crank either treated by a less harsh (but lesser penetrating) process or just have the journals hard chrome plated.

You can re-grind and use a crank, I proved this too on Project Sausage, It's interesting to talk about, but I just wouldn't bother given what I have written above.

[corriedw]

No, you'll need to re-nitride the crank even for the first undersize.

I disagree, all cranks are case hardened in various forms. That mean the deeper you cut it the softer it gets. But in two cases with Alfa cranks I had it cut to the first undersize and done more than 100k km with it. There were never signs of wear(low oil pressure)

On an Uno turbo engine I had to cut it to the second undersize and had the engine open 90k very hard km further. Crank was measured with zero wear. I have a feeling these factory turbo cars from the same company and period, has similar cranks.

[Steve Webb]

I guess the argument is pretty academic anyway, most people don't get a crank reground more than once taking the bearings up to 1 oversize, ( +0.2mm) . I know I wouldn't bother getting a crank reground beyond that. If a crank keeps eating bearings you're going to start wondering whether there is an underlying problem.

[SteveNZ]

I disagree, all cranks are case hardened in various forms. That mean the deeper you cut it the softer it gets. But in two cases with Alfa cranks I had it cut to the first undersize and done more than 100k km with it. There were never signs of wear(low oil pressure)

On an Uno turbo engine I had to cut it to the second undersize and had the engine open 90k very hard km further. Crank was measured with zero wear. I have a feeling these factory turbo cars from the same company and period, has similar cranks.

My comment was just an interpretation of the extract above. When they say "after undersizes" they mean "after the crank has been undersized". Think about it from the automaker's point of view. It is not in their interest to guarantee the hardness after undersizing.

It maybe ok, or not. One thing is for sure, it's not going to be as good as a new or used crank in perfect condition.

As a hobbyist, I've ground a crank or 2 also and never had a problem but that is far from a conclusive test that it will be alright. I'm happy to take risks myself, but to guarantee it to someone else, and even take on the risk in a commercial exercise is something altogether different.

For the record I have also seen 16V engines with ground cranks that have failed.